Observation of Spectral Structures in the Flux of Cosmic-Ray Protons from 50 GeV to 60 TeV with the Calorimetric Electron Telescope on the International Space Station

O Adriani; Y Akaike; K Asano; Y Asaoka; E Berti; G Bigongiari; W R Binns; M Bongi; P Brogi; A Bruno; J H Buckley; N Cannady; G Castellini; C Checchia; M L Cherry; G Collazuol; K Ebisawa; A W Ficklin; H Fuke; S Gonzi; T G Guzik; T Hams; K Hibino; M Ichimura; K Ioka; W Ishizaki; M H Israel; K Kasahara; J Kataoka; R Kataoka; Y Katayose; C Kato; N Kawanaka; Y Kawakubo; K Kobayashi; K Kohri; H S Krawczynski; J F Krizmanic; P Maestro; P S Marrocchesi; A M Messineo; J W Mitchell; S Miyake; A A Moiseev; M Mori; N Mori; H M Motz; K Munakata; S Nakahira; J Nishimura; G A de Nolfo; S Okuno; J F Ormes; S Ozawa; L Pacini; P Papini; B F Rauch; S B Ricciarini; K Sakai; T Sakamoto; M Sasaki; Y Shimizu; A Shiomi; P Spillantini; F Stolzi; S Sugita; A Sulaj; M Takita; T Tamura; T Terasawa; S Torii; Y Tsunesada; Y Uchihori; E Vannuccini; J P Wefel; K Yamaoka; S Yanagita; A Yoshida; K Yoshida; W V Zober; CALET Collaboration

doi:10.1103/PhysRevLett.129.101102

Observation of Spectral Structures in the Flux of Cosmic-Ray Protons from 50 GeV to 60 TeV with the Calorimetric Electron Telescope on the International Space Station

Phys Rev Lett. 2022 Sep 2;129(10):101102. doi: 10.1103/PhysRevLett.129.101102.

Authors

O Adriani^{1

2}, Y Akaike^{3

4}, K Asano⁵, Y Asaoka⁵, E Berti^{1

2}, G Bigongiari^{6

7}, W R Binns⁸, M Bongi^{1

2}, P Brogi^{6

7}, A Bruno⁹, J H Buckley⁸, N Cannady^{10

11

12}, G Castellini¹³, C Checchia^{6

7}, M L Cherry¹⁴, G Collazuol^{15

16}, K Ebisawa¹⁷, A W Ficklin¹⁴, H Fuke¹⁷, S Gonzi^{1

2}, T G Guzik¹⁴, T Hams¹⁰, K Hibino¹⁸, M Ichimura¹⁹, K Ioka²⁰, W Ishizaki⁵, M H Israel⁸, K Kasahara²¹, J Kataoka²², R Kataoka²³, Y Katayose²⁴, C Kato²⁵, N Kawanaka²⁰, Y Kawakubo¹⁴, K Kobayashi^{3

4}, K Kohri²⁶, H S Krawczynski⁸, J F Krizmanic¹¹, P Maestro^{6

7}, P S Marrocchesi^{6

7}, A M Messineo^{7

27}, J W Mitchell¹¹, S Miyake²⁸, A A Moiseev^{11

12

29}, M Mori³⁰, N Mori², H M Motz³¹, K Munakata²⁵, S Nakahira¹⁷, J Nishimura¹⁷, G A de Nolfo⁹, S Okuno¹⁸, J F Ormes³², S Ozawa³³, L Pacini^{1

2

13}, P Papini², B F Rauch⁸, S B Ricciarini^{2

13}, K Sakai^{10

11

12}, T Sakamoto³⁴, M Sasaki^{11

12

29}, Y Shimizu¹⁸, A Shiomi³⁵, P Spillantini¹, F Stolzi^{6

7}, S Sugita³⁴, A Sulaj^{6

7}, M Takita⁵, T Tamura¹⁸, T Terasawa⁵, S Torii³, Y Tsunesada^{36

37}, Y Uchihori³⁸, E Vannuccini², J P Wefel¹⁴, K Yamaoka³⁹, S Yanagita⁴⁰, A Yoshida³⁴, K Yoshida²¹, W V Zober⁸; CALET Collaboration

Affiliations

¹ Department of Physics, University of Florence, Via Sansone, 1-50019 Sesto Fiorentino, Italy.
² INFN Sezione di Florence, Via Sansone, 1-50019 Sesto Fiorentino, Italy.
³ Waseda Research Institute for Science and Engineering, Waseda University, 17 Kikuicho, Shinjuku, Tokyo 162-0044, Japan.
⁴ JEM Utilization Center, Human Spaceflight Technology Directorate, Japan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan.
⁵ Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa, Chiba 277-8582, Japan.
⁶ Department of Physical Sciences, Earth and Environment, University of Siena, via Roma 56, 53100 Siena, Italy.
⁷ INFN Sezione di Pisa, Polo Fibonacci, Largo B. Pontecorvo, 3-56127 Pisa, Italy.
⁸ Department of Physics and McDonnell Center for the Space Sciences, Washington University, One Brookings Drive, St. Louis, Missouri 63130-4899, USA.
⁹ Heliospheric Physics Laboratory, NASA/GSFC, Greenbelt, Maryland 20771, USA.
¹⁰ Center for Space Sciences and Technology, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA.
¹¹ Astroparticle Physics Laboratory, NASA/GSFC, Greenbelt, Maryland 20771, USA.
¹² Center for Research and Exploration in Space Sciences and Technology, NASA/GSFC, Greenbelt, Maryland 20771, USA.
¹³ Institute of Applied Physics (IFAC), National Research Council (CNR), Via Madonna del Piano, 10, 50019 Sesto Fiorentino, Italy.
¹⁴ Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Baton Rouge, Louisiana 70803, USA.
¹⁵ Department of Physics and Astronomy, University of Padova, Via Marzolo, 8, 35131 Padova, Italy.
¹⁶ INFN Sezione di Padova, Via Marzolo, 8, 35131 Padova, Italy.
¹⁷ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan.
¹⁸ Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa, Yokohama, Kanagawa 221-8686, Japan.
¹⁹ Faculty of Science and Technology, Graduate School of Science and Technology, Hirosaki University, 3, Bunkyo, Hirosaki, Aomori 036-8561, Japan.
²⁰ Yukawa Institute for Theoretical Physics, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
²¹ Department of Electronic Information Systems, Shibaura Institute of Technology, 307 Fukasaku, Minuma, Saitama 337-8570, Japan.
²² School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.
²³ National Institute of Polar Research, 10-3, Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
²⁴ Faculty of Engineering, Division of Intelligent Systems Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan.
²⁵ Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
²⁶ Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
²⁷ University of Pisa, Polo Fibonacci, Largo B. Pontecorvo, 3-56127 Pisa, Italy.
²⁸ Department of Electrical and Electronic Systems Engineering, National Institute of Technology (KOSEN), Ibaraki College, 866 Nakane, Hitachinaka, Ibaraki 312-8508, Japan.
²⁹ Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA.
³⁰ Department of Physical Sciences, College of Science and Engineering, Ritsumeikan University, Shiga 525-8577, Japan.
³¹ Faculty of Science and Engineering, Global Center for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.
³² Department of Physics and Astronomy, University of Denver, Physics Building, Room 211, 2112 East Wesley Avenue, Denver, Colorado 80208-6900, USA.
³³ Quantum ICT Advanced Development Center, National Institute of Information and Communications Technology, 4-2-1 Nukui-Kitamachi, Koganei, Tokyo 184-8795, Japan.
³⁴ College of Science and Engineering, Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo, Sagamihara, Kanagawa 252-5258, Japan.
³⁵ College of Industrial Technology, Nihon University, 1-2-1 Izumi, Narashino, Chiba 275-8575, Japan.
³⁶ Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
³⁷ Nambu Yoichiro Institute for Theoretical and Experimental Physics, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
³⁸ National Institutes for Quantum and Radiation Science and Technology, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
³⁹ Nagoya University, Furo, Chikusa, Nagoya 464-8601, Japan.
⁴⁰ College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan.

PMID: 36112450
DOI: 10.1103/PhysRevLett.129.101102

Abstract

A precise measurement of the cosmic-ray proton spectrum with the Calorimetric Electron Telescope (CALET) is presented in the energy interval from 50 GeV to 60 TeV, and the observation of a softening of the spectrum above 10 TeV is reported. The analysis is based on the data collected during ∼6.2 years of smooth operations aboard the International Space Station and covers a broader energy range with respect to the previous proton flux measurement by CALET, with an increase of the available statistics by a factor of ∼2.2. Above a few hundred GeV we confirm our previous observation of a progressive spectral hardening with a higher significance (more than 20 sigma). In the multi-TeV region we observe a second spectral feature with a softening around 10 TeV and a spectral index change from -2.6 to -2.9 consistently, within the errors, with the shape of the spectrum reported by DAMPE. We apply a simultaneous fit of the proton differential spectrum which well reproduces the gradual change of the spectral index encompassing the lower energy power-law regime and the two spectral features observed at higher energies.